1. Field of the Invention
The present invention relates to a hot-water type heating apparatus having a flow rate control valve for controlling a flow rate of hot water. The hot-water type heating apparatus is suitable for an air conditioning apparatus for a vehicle.
2. Description of Related Art
Conventionally, a flow rate of hot water flowing through a heating heat exchanger is controlled to control a temperature of air blown toward a passenger compartment. The applicant proposes a hot-water type heating apparatus as described in JP-A-8-118943. In the hot-water type heating apparatus, a flow rate control valve for controlling the flow rate of hot water is integrated with a heating heat exchanger, an inlet side tank through which hot water controlled by the flow rate control valve flows into the heating heat exchanger is disposed at a lower side of the heating heat exchanger, and an outlet side tank is disposed at an upper side thereof. In the heating heat exchanger, hot water flows in one way from a lower side toward an upper side of the core portion; and therefore, air contained in hot water can be smoothly discharged to the outside of the heating heat exchanger. However, when the flow rate of hot water flowing through the heating heat exchanger is controlled at a minute flow rate, air blown from the heating heat exchanger has a different temperature distribution in a left-right direction (i.e., a longitudinal direction of tank) of the heating heat exchanger. As a result, the temperature of air blown toward a right side in the passenger compartment is different from the temperature of air blown toward a left side in the passenger compartment. To overcome the problem, in the hot-water type heating apparatus, a hot-water distribution unit for uniformly distributing hot water in the heating heat exchanger in the left-right direction is provided in the inlet side tank or the outlet side tank. That is, a pipe-like member extending in the longitudinal direction of the tank is provided in the inlet side tank. The pipe-like member has a plurality of hot water holes through which hot water distributes within the inlet side tank.
However, in the above-described hot-water type heating apparatus, hot water is supplied to the inlet side tank of the heating heat exchanger through the hot water holes provided in the pipe-like member even during the maximum heating mode where the flow rate control valve controls the flow rate of hot water at the maximum flow rate. Therefore, a flow resistance of hot water becomes higher, hot water supplied to the heating heat exchanger is restricted, and thereby reducing the maximum heating capacity for the passenger compartment.